The common image compression technology loses high frequency components of an image due to a high image compression ratio. And when the image is decompressed, a mosquito noise is incurred in the high frequency area, for example, at an edge of the image as illustrated in FIG. 1. In the prior art, a low-pass filter is utilized to remove the mosquito noise. However, when the strength of the filter is too strong, the image becomes fuzzy and the image details are damaged. Conversely; when the strength of the filter is too weak, the mosquito noise cannot be removed effectively.